Alternator-Starter-Junction Block Wiring 84 K30

[Tance52]

I’m having trouble with the wiring between the alternator-starter-firewall junction block on a 1984 K30 (previously a military diesel, now a 454). I figured out the junction block with the help of a previous post, but now I’m trying to wire it from scratch and the prints I have are confusing. So before I burn it to the ground I’d like to get some experienced opinions on whether my interpretation of the prints is correct. Thanks in advance for your replies.

[Dead Parrot]

The CUCVs came with a 24V setup. Unless the person that did the 454 install removed all the 24V bits, you may have leftover wires that will cause confusion. There were a several relays under the dash that a normal K30 didn't have.

The alternators were also different from the normal 12V civilian K30s. The CUCVs had two 12v alternators.

Assuming a normal 12SI type, the red wire(voltage sense) of the two wire connector normally goes to the junction block. The brown wire will either go to a resistor for a gauge equipped truck or to the idiot light. The CUCVs came with two idiot lights, one for each alt.

Your wire gauges sizes seem too small. I think the purple wire on my CUCV was 8 guage. The alt main wires should be 10 gauge minimum and larger if your alt is rated more then 70 amps. The wire from bat term on solenoid to junction block should also be 8 gauge. You should be able to delete the bat to junction block wire as the j-block gets its power from the bat term on the solenoid.

Be sure to include fusible links on your wires.

[hatzie]

Download the 1984 Civilian wiring diagrams and find the CUCV Tech Manuals "TMs" on Steel Soldiers.

The alternator BAT (Charge) wire should be 10ga. You can run this to the firewall junction studs. You'll need a 10ga wire from the firewall junction studs to the starter BAT terminal with a 12ga fusible link at the starter.

The Ignition main power feed wire should be run to the firewall junction studs using 10ga.
Alternator regulator sense terminal 2 should be 12ga to the Starter BAT terminal. This should have a 14ga fusible link at the starter.


The alternator regulator exciter terminal 1 can be run in one of two ways.

1. Liberate a 47Ω resistance wire from a squarebody junker that was equipped with gauges from the alternator plug to the bulkhead and the wire that runs from the bulkhead to the Ignition switched hot. Extract the terminals so you keep the entirety of both wires.
2. Your other option is to run this your own wire through the bulkhead to a warning bulb in the instrument panel or use one of the GEN lamp wires from the DOD wiring. If you're using a civilian gauge panel you can use the SEAT BELT bulb. The bulb needs an ignition switched HOT and the alternator exciter wire. If you're using this method you can use 16ga wire. The bulb is the easiest way to wire this.

18ga wire will carry the solenoid energize current for the Purple CRANK wire but for mechanical durability I'd use 16ga wire. You should run this circuit through the Neutral-start/backup-lamp switch at the base of the steering column then out through the bulkhead plug. IIRC the ignition switch to neutral-start switch is Yellow then Purple the rest of the way.

Use SXL jacketed wire.

[Tance52]

Thanks Parrot and Hatzie for the responses, I appreciate the help. Kind of a mutt electrical system... ex-military, ex-diesel 24v, converted to 12v 454. Your inputs will help me get the electrical finished and get it running after major surgery. It's a beast... the last of the straight axles and this one is a plug-and-play monster truck with those huge HD axles and ex-dually suspension. I say "ex-dually" because I put a regular bed and 16.5 super singles on the rear with 37s all around.

[Dead Parrot]

Rule 1 with CUCV wiring is trust nothing until you have verified it. An example of something I found on mine: The 24V purple wire was cut on the engine side of the firewall just out of the fuse block connector. It was still hot and not taped. A 12V wire was ran off of the ignition switch and though the firewall to the other side of the purple wire. The starter was a 12v starter with 24V to the battery terminal of the solenoid and 12V for the solenoid start terminal. It was a bypass for a failed start relay under the dash. According to the paperwork I received from the last seller, this was done by an automotive repair shop while the truck was owned by a rural Fire Department.

It took a bit of puzzling things out to get it restored back to a 24V starting setup as that seemed simpler since both batteries and both alternators are still present.

[kwmech]

Eliminate the 14ga wire going to the starter from the junction block. Connect the 16ga wire going to the starter from the fuse block to the junction block. The only 12v you need down there is the battery cable. The batt cable from the Alt should be at least 10ga or preferred 8ga now-a days and goes directly to the battery, no need to connect it to the junction block. Eliminate the splice from there and connect that to the junction block also.

Battery to junction block should be 12ga with a fusible link

[hatzie]

The Civilian trucks usually have three connections on the starter BAT stud, and sometimes four.
Stock

1. 4ga battery + cable.
2. 12ga Power feed to the junction studs through a fusible link.
3. 14ga Power for the headlamp switch through a fusible link.
4. 14ga Sense to the Alternator through a fusible link.

The Civilian Junction studs usually have the following three or four connections stock.

1. 12ga Circuit 2 Feed to the cab through a fusible link.
2. 12ga alternator BAT stud main charge wire through a fusible link.
3. 14ga AC blower HI through a fusible link.
4. Sometimes trailer connector 12ga battery wire through a fusible link or a 50A circuit breaker.

Bumping up one wire gauge doesn't hurt a thing.

The CUCV has a 24v/12v hybrid electrical system and the OP is trying to morph it into a regular 12v rig.

[Tance52]

Well I think I incorporated your recommendations and changes into a final sketch, let me know if anyone sees a problem. As Parrot pointed out, I plan to delete the battery-to-junction block wire since the junction block will always be hot from the starter solenoid connection. Thanks again for your assistance!